Diffusion Sliver as a response

[Mattao19]

Say somebody {Doom Blades} my {Manaweft Sliver} and in response I {Chord of Calling} for {Diffusion Sliver} (not showing up but it makes all my slivers turn into {Frost Titan}) do they have to pay the extra 2?

[Remillo]

Nope.  The Diffusion Sliver has the actually be on the field when the spell is cast, because that's when it's 'becoming a target of'.  If it's already on the stack, it's too late...  Unless you can somehow redirect the spell to a new sliver.